The invention relates to a method of regenerating activated carbon by the decomposition of adsorbed, organic material in the presence of water and oxygen.
The use of activated carbon as an adsorption and filter material, particularly in the purification of drinking water and waste water and in the food industry, is well known. Therefore, the regeneration of activated carbon adsorbents is of great importance in view of its widespread use.
Activated carbon may be regenerated by thermal regeneration, wherein the adsorbent is heated to about 800.degree. C. to 900.degree. C., possibly with the simultaneous addition of water vapor. During thermal regeneration processes, however, losses of between 3% and 15% of activated carbon are common. The regenerated product often exhibits an adsorption capacity which is reduced to 80% of the initial value. This reduction occurs because the smallest pores, in particular, which are able to retain molecules up to a molecular weight of 500, are destroyed during the thermal regeneration process. With the thermal regeneration method, which can only be used with granular activated carbon and not with comparatively cheap pulverized activated carbon, both the direct loss of activated carbon and that of adsorption capacity must be compensated for. For example, after six regeneration cycles, a carbon filter must generally be completely charged with fresh carbon.
The regeneration of activated carbon by chemical oxidation (e.g., with permanganate) is effected at room temperature, but is without practical significance because the chemical oxidants are not easily introduced, if at all, into the smallest pores of the activated carbon. Thus these pores often become blocked so that the regeneration is not completely effective.
Biological regeneration of activated carbon in the preparation of drinking water and waste water renders possible the removal of deposited and adsorbed materials which can be decomposed biologically. However, refractory organic substances which cannot be decomposed biologically have to be removed from the pores of the activated carbon by another method of regeneration.
A regeneration of activated carbon which is loaded with organic materials and which can be carried out at room temperature in the presence of water and oxygen (e.g., from air) by means of .gamma.-rays, is described in U.S. Pat. No. 3,846,296. In the process described in that patent, waste water which has previously been biologically treated and passed through a sand filter is forced through a radiation container of stainless steel partially filled with activated carbon to which compressed air is supplied near the bottom. Ordinary commercial activated carbon from coal, oil sludge, wood or coconut shells with a relatively large surface is used. A .gamma.-ray-source with radioactive isotopes such as .sup.60 Co or .sup.137 Cs is located in the upper central portion of the container.
In order to be able to cleanse the activated carbon of sand and other solid substances at various time intervals, a high-pressure water rinse line is connected to the radiation container and enables the activated carbon to be cleansed. This gamma radiation regeneration process renders possible a continuous regeneration of the activated carbon. Practical use of this method is rendered difficult, however, by safety measures necessitated by the use of the radioactive isotopes. The radiation sources must be checked for tightness at certain intervals and be renewed, which generally has to be carried out by specialized personnel. The level of radiation cannot be adapted to the amount of material to be irradiated. The gamma ray dose necessary for the regeneration of the activated carbon can only be regulated by altering the speed at which the material to be irradiated passes through the radiation regeneration chamber.